GENEVA, March 20 (Reuters) - Jewels belonging to Lily Safra, billionaire widow of banker Edmond Safra, are estimated to fetch more than $20 million at a May auction whose proceeds will benefit 20 charities selected by the philanthropist, Christie’s said on Tuesday.

The 70 gems, being offered at its Geneva sale on May 14, include diamonds, rubies and sapphires as well as antique pieces dating to the late 18th-century and period jewellery, it said.

“This jewellery collection reflects her refined taste and its evolution throughout five decades, from the 1970s to the present day,” Christie’s said in a statement.

Eighteen pieces are designed by Paris-based American jeweller Joel Arthur Rosenthal, known as JAR, making it “the largest private collection of creations by JAR ever to be offered at auction”, it said.

The majority were designed specifically for the Brazilian-born socialite over the last three decades by JAR, who produces about 70-80 works a year for an exclusive clientele, Christie’s spokesman Cristiano De Lorenzo said.

They include a ruby and diamond Camellia flower brooch, created for Lily Safra in 2003, estimated to fetch $1.2 million to $1.5 million, he said.

The brooch embodies JAR’s hallmark technique of setting small stones closely together to form a pavement of jewels.

“It must be an exceptional collection because Lily Safra and her late husband Edmond not only had unlimited means but excellent taste in art,” Eric Valdieu, an independent jewellery dealer based in Geneva, formerly of Christie‘s, told Reuters.

Lily Safra sold artwork, furniture, silver and decorative objects from the couple’s collection at rival Sotheby’s last June, raising some $45 million.

But Valdieu said it was logical that she consigned her jewels to Christie‘s, owned by French billionaire Francois Pinault, given the Safras’ close ties of over 30 years with Francois Curiel, international head of its jewellery department.

“After Liz Taylor, Lily Safra - emblematic collections are now being dispersed,” said Valdieu, who is also a fund manager for the Luxembourg-based investment fund Divine Jewels.

The Safra couple is known for their philanthropic work, including building Jerusalem’s Safra Square and donations to the Louvre in Paris, where a gallery bears their name.

Designated beneficiaries of the jewellery sale’s proceeds include Elton John AIDS Foundation, the Royal Opera House in London and several institutions researching Parkinson‘s, a neurodegenerative disease which Edmond Safra had.

The Lebanese-born billionaire and banking scion who owned Republic National Bank of New York, died in a mysterious fire in his penthouse flat in Monaco in December 1999. His American male nurse Ted Maher was convicted of the arson death in 2002.

Lily Safra, who had three previous husbands, divides her time between London, New York, Geneva and Monaco. She clocked in at No. 1,015 on Forbes 2012 list of the world’s billionaires with a net worth of $1.2 billion.

The “Beau Sancy”, a diamond coveted by kings, queens and princes for centuries, used to reinforce alliances between nations and pawned to pay off royal debts goes on sale at Sotheby’s in Geneva on May 15.